The present invention generally relates to a vehicle wheel suspension system and, more particularly, to an independent rear wheel suspension for motor vehicles.
The Japanese Laid-open Patent Publication laid open to public inspection under No. 49-26921 in 1974 discloses a vehicle rear wheel suspension having a construction as shown in FIG. 1 of the accompanying drawings. Referring to FIG. 1 of the accompanying drawings, wherein the only lefthand rear wheel and its suspension are diagrammatically shown as viewed from top of the vehicle, the prior art rear wheel suspension comprises a wheel carrier 1 having a wheel journal or axle for the support of a rear wheel 2 for rotation independently of the wheel carrier 1 and operatively coupled to a vehicle superstructure, particularly a chassis 4, by means of an arm member 3 which extends in a direction generally transversely of the vehicle superstructure and is operatively interposed between the wheel carrier 1 and the chassis 4. The arm member 3 is comprised of a stub 3a and a pair of forked front and rear arms 3b and 3c, it being to be understood that the terms "front" and "rear" referred to above and hereinafter throughout the specification and the appended claims are used to denote respective positions defined in terms of the vehicle superstructure. The stub 3a has a free end hingedly and yieldingly connected to a lateral portion of the chassis 4 while respective free ends of the front and rear arms 3b and 3c, which are forked from the stub 3a, are hingedly and yieldingly connected at A and B to front and rear portions of the wheel carrier 1 by means of associated rubber bushings. The prior art rear wheel suspension further comprises a tension rod 5 having one end hingedly and yieldingly connected to a front portion of the chassis 4 and the other end hingedly and yieldingly connected to a portion of the arm 3b adjacent the wheel carrier 1.
The prior art rear wheel suspension having the construction shown in FIG. 1 has some disadvantages. By way of example, when a load P acting in a direction rearwardly of the vehicle superstructure is applied to the area of contact of the wheel 2, particularly the tire on the wheel 2, to the road surface as the wheel encounters irregularities in the road, the rubber bushings used at the various joints undergo elastic deformation to such an extent that the arm member 3 is rearwardly displaced from the position shown by the solid lines to the position shown by the broken lines, causing the wheel 2 to point outwards, that is, to toe out, rather than to point straight ahead, and the joints A and B are consequently displaced to the respective positions shown by A' and B'. This tendency of the wheel 2 to toe out not only has an adverse influence on the tire, but also adversely affects the riding quality of the vehicle as is well known to those skilled in the art. This tendency of the wheel 2 to toe out is increased if the wheel carrier 1 is made easily displaceable relative to the chassis 4, which in turn adversely affects not only the ease of steering, but also the steering stability particularly during the running of the vehicle over a irregular road.
A similar phenomenon occurs during the cornering of the vehicle, that is, during the turning of the vehicle in a direction either leftwards or rightwards. More specifically, during the cornering of the vehicle along a curve, the outer wheel rotates on or follows a path having a larger radius than the path of the inner wheel resulting in increased pressure of contact of the outer wheel with the road surface while the vehicle superstructure tilts laterally under the influence of centrifugal force and, at this time, the various elastic bushings used at the various joints of the arm member 3 are elastically deformed to such an extent as to increase the tendency of the wheel 2 to toe out. This results in over-steerability, that is, the steering stability is adversely affected. This also happens even when the wind blows the vehicle in a direction transversely of the vehicle during the running of the vehicle.
A rear wheel suspension wherein the front and rear arms, corresponding to the arms 3b and 3c shown in FIG. 1, extend from the wheel carrier in substantially parallel relation to each other to different lateral portions of the vehicle chassis is well known and is disclosed, for example, in the Japanese Patent Publication No. 51-21494 published for opposition on July 2, 1976. Even this type of rear wheel suspension has a type disclosed in the Japanese Patent Publication disadvantages similar to those described in connection with the rear wheel suspension having the construction shown in FIG. 1.
A rear wheel suspension wherein the front and rear arms, which are separate from each other, have different lengths and extend parallel or approximately parallel to each other is disclosed in U.S. Pat. No. 3,759,542, patented on Sept. 18, 1973. With the construction disclosed in this U.S. patent, for a slight displacement of the wheel, the tendency of the wheel to toe in is small. Where the amount of the toe-in of the wheel is desired to be increased, the difference in length between the front and rear arms must be larger for the limited space available for the installation of the wheel suspension.